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A technique is described to study simultaneously the adsorption and desorption of colloidal particles on collector surfaces in a parallel plate flow chamber. Using a phase contrast microscope equipped with an ultra long working distance objective, the deposition process can be observed in situ. Analysis of successively stored images yields the time of arrival and departure of each colloidal particle, thus enabling determination of the adsorption and desorption rates, as well as of the total number of particles deposited. In addition the method allows analysis of the spatial arrangement of deposited particles, while distinguishing between upstream and downstream deposition of particles, yielding pair distribution functions, going from -180 ° to + 180 °. In this paper the technique has been applied to study the deposition of 736-nm diameter monodisperse polystyrene latex particles from a potassium nitrate solution ( 1 and 60 raM) to glass, using varying flow rates (0.034 to 0.456 cm 3. s-l). Initial deposition rates J0 were derived from the total number of adhering particles n (t) as well as from the experimentally measured time dependence of the deposition rate j(t). The results showed clear tendencies with ionic strength and flow rate. The desorption ratesjdes(t) were small and the desorption rate coefficients/3 were dependent on the residence times of the adhering particles. The blocked areas, derived from the deposition kinetics, ranged from 8 to 675 times the geometrical cross section of a particle, depending on the experimental conditions.

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